Catalytic Studies on Tryptophanase fromBacillus alvei

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Abstract
Tryptophanase fromBacillus alveiexhibited the expected spectrum of pyridoxal-5′-phosphate-dependent reactions. It exhibitedl-serine dehydratase,S-alkyl-cysteine lyase, and cysteine desulfhydrase activities, as well as the classic tryptophanase reactions (all beta elimination reactions). It also acted as a tryptophan synthetase (beta replacement reactions) using indole plusl-serine orl-cysteine orS-methyl-cysteine as substrates. The beta elimination reactions are simple competitors of the replacement reactions for the same amino acid substrates. The kinetics of the reactions were examined in detail using a coupled continuous spectrophotometric assay. A product (indole) inhibition study of the beta elimination reaction with tryptophan showed simple, noncompetitive inhibition; the same study with allosubstrates showed noncompetitive inhibition by indole. These product studies provided data on the beta replacement reactions as well. The results are discussed in terms of a mechanism for theB. alveitryptophanase.

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